Thermal energy is produced by many industrial, assembly, and manufacturing processes. Automobiles, small equipment, and heavy equipment also produce thermal energy. Some of this thermal energy is waste heat, which is heat produced by machines, electrical equipment, and industrial processes for which no useful application is found or planned, and is generally a waste by-product. Waste heat may originate from machines, such as electrical generators, or from industrial processes, such as steel, glass, or chemical production. The burning of transport fuels also contributes to waste heat.